Generally, an annealing method varies such as a furnace annealing using heat treatment furnace, a rapid thermal annealing (RTA) using radiant heat of halogen lamp and the like, a laser annealing using laser, a annealing using Joule heating, etc.
These annealing methods are selected adequately considering the characteristic of material and process in point of a temperature range of annealing, uniformity of annealing temperature, heating rate, cooling rate, purchase price, maintenance cost, etc. Especially, selectable heat treating methods are extremely restricted in case of requiring high temperature annealing or rapid annealing at a local region of material due to the characteristic of the material and process.
Among the above annealing methods, the laser annealing method can carry out the rapid annealing on the surface of a material, but because the possibility of annealing is decided by kinds of wavelength of laser and heat treatment-requiring material, the material able to annealing has been limited. Particularly, in case of annealing to large-size, the line beam-typed laser should be scanning repeatedly, thus problems such as non-uniformity of laser beam intensity and irradiation dosage of laser beam itself over time can be occurred. Furthermore, the method is disadvantageous in that not only the price of equipment but also maintenance cost is extremely high.
Although the RTA method is widely used in preparation process of a semiconductor, the present technology is applied only to silicon wafer of 300 mm in diameter, so that it has a limit in annealing uniformly on broader substrate than that. In addition, due to having a maximum heating rate of 400° C./sec, it is impossible to use in a process requiring higher heating rate than that.
Therefore, a lot of researches are being conducted for annealing method which may solve such problems and free from the limit of process. Among theses research, as described in KP 2004-74493 of the applicant, there is the rapid annealing method through Joule heating by application of an electric field to a conductive layer, and the above annealing method makes possible a selective rapid annealing over a desired material by means of heat conduction of an generated intense heat, and it could be expected to have much higher heating rate than that of RTA process.
However, there is a limit in application of the annealing method using Joule heating by an electric field application as well as the above application, due to having not been clearly identified the cause of physical phenomenon such as generation of arc during Joule heating.